As the communications industry continues to evolve, ever-increasing demand for high-speed broadband solutions for communications will result, with the accompanying technologies experiencing a similar demand pattern. While industry analysts predict that 100-megabit speeds will be common by the year 2002, the disclosed system design can assist in delivering these speeds now.
The need for high-speed Internet access within the United States is well defined. With respect to Internet applications alone, as of December 1999, there were fewer than 250,000 U.S. customers purchasing DSL services, as compared to more than 30 million Internet customers. The ever-increasing need for wireless communication services such as Cellular Mobile Telephone (CMT), Digital Cellular Network (DCN), Personal Communication Services (PCS) and the like, typically requires the operators of such systems to serve an ever-increasing number of users in a given service area. As a result, certain types of base station equipment including high capacity Broadband Transceiver Systems (BTS) have been developed, which are intended to service a relatively large number of active mobile stations in each cell. Such BTS equipment can typically service, for example, ninety-six simultaneously active mobile stations in a single four feet tall rack of electronic equipment. This base station equipment typically costs less than $2000 to $4000 per channel to deploy, and so the cost per channel serviced is relationally low. However, demand is increasing beyond capacity and downward cost pressures continue to exist.
Numerous patents have attempted to solve these problem such as U.S. Pat. No. 5,970,410 issued to Carney, et al. on Oct. 19, 1999, titled “Cellular System Plan Using In Band-Translators To Enable Efficient Deployment Of High Capacity Base Transceiver Systems” describes a wireless system architecture whereby high efficiency broadband transceiver systems can be deployed at an initial build out stage of the system in a cost-efficient manner. A home base station location is identified within each cluster of cells, and rather than deploy a complete suite of base station equipment at each of the cells in the cluster, inexpensive translator units are located in the outlying cells serviced by the home base station in which low traffic density is expected. The translators are connected to directional antennas arranged to point back to the home base station site. The translators are deployed in such a way that they mesh with the eventually intended frequency reuse for the entire cluster of cells. The translator to base station radio links operate in-band, that is, within the frequencies assigned to the service provider; for example, the available frequency bands are divided into at least two sub-bands, with a first sub-band assigned for use as a home base station to translator base station communication link, and a second sub band is assigned for use by the mobile station to translator communication link. If desired, a third sub-band can then be used for deployment of base transceiver systems in the conventional fashion where the base station equipment located at the center of a cell site communicates only with mobile stations located within that cell. When coupled with efficient frequency reuse schemes, maximum efficiency in densely populated urban environments is obtained. According to some arrangements, the cells are each split into radial sectors and frequencies are assigned to the sectors in such a manner as to provide the ability to reuse available frequencies. Although frequency reuse schemes can be highly efficient, it requires at least two complete sets of multi-channel transceiver equipment such as in the form of a Broadband Transceiver System (BTS) to be located in each cell.
Nevertheless, when a wireless system first comes on line, demand for use in most of the cells is relatively low, and it is typically not possible to justify the cost of deploying complex multi-channel BTS equipment based only upon the initial number of subscribers. Because only a few cells at high expected traffic demand locations (such as at a freeway intersection) will justify the expense to build-out with high capacity BTS equipment, the service provider is faced with a dilemma. The provider can build-out the system with less expensive narrowband equipment, initially, to provide some level of coverage, and then upgrade to the more efficient equipment as the number of subscribers rapidly increases in the service area; however, the initial investment in narrowband equipment is then lost. Alternatively, a larger up-front investment can be made to initially deploy high capacity equipment, so that once demand increases, the users of the system can be accommodated without receiving busy signals and the like, although this has the disadvantage of carrying the money cost of a larger up front investment.
Other various techniques for extending the service area of a given cell have been proposed. For example, U.S. Pat. No. 4,727,490 issued to Kawano, et al. and assigned to Mitsubishi Denki Kabushiki Kaisha, discloses a mobile telephone system in which a number of repeater stations are installed at the boundary points of hexagonally shaped cells. The repeaters define a small or minor array that is, in effect, superimposed on a major array of conventional base stations installed at the center of the cells. With this arrangement, any signals received in so-called minor service areas by the repeaters are relayed to the nearest base station.
Another technique is disclosed in U.S. Pat. No. 5,152,002 issued to Leslie, et al., wherein the coverage of a cell is extended by including a number of so-called “boosters” arranged in a serial chain. As a mobile station moves along an elongated area of coverage, it is automatically picked up by an approaching booster and dropped by a receding booster. These boosters, or translators, use highly directive antennas to communicate with one another and thus ultimately via the serial chain with the controlling central site. The boosters may either be used in the mode where the boosted signal is transmitted at the same frequency as it is received or in a mode where the incoming signal is retransmitted at a different translated frequency.
Additional attempts to improve coverage include spectral efficiency schemes such as disclosed in U.S. Pat. No. 5,592,490 issued to Barratt, et al., on Jan. 7, 1997 titled “Spectrally Efficient High Capacity Wireless Communication Systems” which discloses a wireless system comprising a network of base stations for receiving uplink signals transmitted from a plurality of remote terminals and for transmitting downlink signals to the plurality of remote terminals using a plurality of conventional channels including a plurality of antenna elements at each base station for receiving uplink signals, a plurality of antenna elements at each base station for transmitting downlink signals, a signal processor at each base station connected to the receiving antenna elements and to the transmitting antenna elements for determining spatial signatures and multiplexing and demultiplexing functions for each remote terminal antenna for each conventional channel, and a multiple base station network controller for optimizing network performance, whereby communication between the base stations and a plurality of remote terminals in each of the conventional channels can occur simultaneously.
Other methods include specialized propagation techniques such as shown in U.S. Pat. No. 6,058,105 issued to Hochwald, et al. on May 2, 2000 titled “Multiple Antenna Communication System and Method Thereof” which discloses a communications system that achieves high bit rates over an actual communications channel between M transmitter antennas of a first unit and N receiver antennas of a second unit, where M or N>1, by creating virtual sub-channels from the actual communications channel. The multiple antenna system creates the virtual sub-channels from the actual communications channel by using propagation information characterizing the actual communications channel at the first and second units. For transmissions from the first unit to the second unit, the first unit sends a virtual transmitted signal over at least a subset of the virtual sub-channels using at least a portion of the propagation information. The second unit retrieves a corresponding virtual received signal from the same set of virtual sub-channels using at least another portion of said propagation information.
Unfortunately, each of these techniques has their difficulties and add additional costs and complexities to the system. With the method that uses an array of repeaters colocated with the primary cell sites, the implementation of diversity receivers becomes a problem. Specifically, certain types of cellular communication systems, particularly those that use digital forms of modulation, are susceptible to multi-path fading and other distortion. It is imperative in such systems to deploy diversity antennas at each cell site. This repeater array scheme makes implementation of diversity antennas extremely difficult, since each repeater simply forwards its received signal to the base station, and diversity information as represented by the phase of the signal received at the repeater, is thus lost.
The booster scheme works fine in a situation where the boosters are intended to be laid in a straight line along a highway, a tunnel, a narrow depression in the terrain such as a ravine or adjacent a riverbed. However, there is no teaching of how to efficiently deploy the boosters in a two-dimensional grid, or to share the available translated frequencies as must be done if the advantages of cell site extension are to be obtained throughout an entire service region, such as a large city.
Shielding systems for particular circuits are also well known in the prior art. For example, U.S. Pat. No. 5,475,876 issued to Terada, et al. on Dec. 12, 1995, titled “Tuner Unit Having Electromagnetically Isolated UHF And VHF Section With No Noise” discloses a tuner unit including an antenna input filter section, a UHF section, a VHF section, and a PLL section which are electromagnetically separated by walls, an inductor for a VHF local oscillator is disposed adjacent to the UHF section, and is electromagnetically separated by a subdivision wall from the UHF section and the VHF section. Also, U.S. Pat. No. 5,671,220 issued to Tonomura on Sep. 23, 1997, titled “Satellite Channel Interface In Indoor Unit Used For Satellite Data Communication” discloses a Satellite Channel Interface (SCI) that is constituted by an analog section having a multiplexer unit and a down converter unit, and a digital section constituted by a modulator-demodulator unit. The Satellite Channel Interface has a single printed circuit board on which all of the above units are formed. A rectangular member surrounds the analog section, and a shield cover shields an opening portion of the rectangular member. The single printed circuit board is a multi-layered board constituted by at least three conductive layers, of which the bottom two layers are grounding electrodes. The SCI does not require the terminals and cables which are otherwise necessary, can be made compact, and can be manufactured with the reduced number of processing steps.
Additionally, shielding for devices has been used such as in U.S. Pat. No. 5,564,096 issued to Hama, et al. on Oct. 8, 1996, which discloses a portable radio communication device such as wristwatch receiver and/or transmitter that is provided with an effective noise shielding structure. The portable radio communication device includes a high frequency analog circuitry for receiving and transmitting radio signals and further includes digital circuitry for data processing and display. The noise shielding structure protects high frequency noise from being transmitted to the analog circuitry from the digital circuitry and from other outside sources. The noise shielding structure is made of electrically conductive material. In another aspect of the invention, at least one circuit board constructed of a multi-layered construction having at least one inner printed wire pattern is provided. The inner printed wire pattern is set at ground potential with respect to the high frequency output from the analog circuitry. In this manner the inner printed wire pattern serves as a noise shielding member. In addition, the invention obtains effective noise shielding without increasing the size or the manufacturing cost of the device.
A similar device shielding use is shown in U.S. Pat. No. 5,124,889 issued to Humbert, et al. on Jun. 23, 1992, “titled Electromagnetic Shielding Apparatus For Cellular Telephones” that discloses an electromagnetic shielding apparatus for portable telephones and other electronic equipment, includes shield clips for intercoupling the conductive surfaces of a housing to the metal layer of the circuit board. Each shield clip mates with a corresponding edge of the circuit board such that tabs insert into holes in the central channel of the clip and feet of the clip rest on other tabs. The clip is bonded to the metal layer of the circuit board preferably by resistance welding, thereby reliably connecting the clip and the conductive housing surfaces to signal ground.
Finally, U.S. Pat. No. 5,777,856 issued to Phillips, et al. on Jul. 7, 1998, titled “Integrated Shielding And Mechanical Support” discloses an integrated shielding and mechanical support that simultaneously addresses the problems of providing RF shielding for an electronic device such as a radio transceiver and providing a rigid mechanical assembly for the electronic device. Two conductive rails hold together multiple Printed Circuit Boards (PCBs) having conductive layers to produce a four-sided shielding box that protects certain electronic circuits on the PCBs from electromagnetic interference. An internal conductive shield subdivides the inside of the shielding box to provide additional protection for sensitive circuitry. The shielding box inserts into an opening in a five-sided housing section using, which simplifies assembly of PCBs in the housing and facilitates automated assembly. A second housing section attaches to the shielding box once it is inserted into the five-sided housing section.
None of the above patents disclose an effective shielding system allowing for collocation of multiple radio transceivers. Therefore, a need exists for a shielding system for a wireless communications system which achieves high bit rates in a cost effective and relatively simple manner.
It is therefore clear that a primary object of this invention is to advance the art of high-speed wireless Internet access system design. A more specific object is to advance said art by providing an improved shielding design for radio deployment systems usefull for high-speed wireless Internet access.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds. The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.